The invention relates to implants for devices intended for stabilizing the spine.
Devices intended for correcting deformations of the spine and for stabilizing it comprise metal rods which extend along the spine and pass through orifices formed in one end of connection elements which are themselves fastened to the vertebrae via their other end, shaped like a hook, or are screwed into these vertebrae via a threaded end. The rod is immobilized inside the orifice, for example by means of a threaded plug.
In some cases, the orifice through which the rod passes is situated substantially in the continuation of the longitudinal axis of the connection element. In other cases, the connection element is configured in such a way as to laterally offset the longitudinal axis of the connection element relative to the orifice passed through by the rod. This element is then referred to by the term xe2x80x9clateral offset connectorxe2x80x9d.
The document U.S. Pat. No. 5,476,463 describes such a lateral connector with lateral offset. It is made up of a one-piece component comprising a head through which the rod is intended to pass and is connected to a lateral stem provided with an oblong opening intended to be passed through by a screw implanted in a vertebra. In this type of connector, the orientation of the stem in relation to the head is fixed by construction and cannot be modified. To obtain an implantation of the connection elements approximating to the desired optimum, it is therefore necessary for the surgeon to have a range of connectors available whose stems have different orientations and lengths. The need to select them one by one slows down the implantation of the correction device. Moreover, the inevitable limitation on the number of orientations and lengths available for the lateral stem does not always permit optimum implantation of the connection element on the vertebrae. In particular, the site of fixation of the connection element may not always be the one which is the most favourable to the patient. This is especially true when the correction device is implanted in the cervical area, where the vertebrae are small and have a tortuous shape, leaving few locations favourable to the fixation of an implant, particularly of a screw.
Moreover, some devices of the type described above only permit positioning of the connection screw after the connector has been placed on the rod. The site of fixation of the screw is thus completely forced on the surgeon, which makes fitting awkward and often inappropriate to the anatomy of the patient.
It has been proposed, as in document U.S. Pat. No. 5,534,002, to form lateral offset connectors in two parts. The first part is made up of a component intended to be passed through, on the one hand, by the rod and, on the other hand, by an end of a lateral stem constituting the second part of the connector and of which the other end has an opening intended to be passed through by a fixation screw. The engagement of the lateral stem in the component can be controlled by the surgeon, and the member for immobilizing the rod in the component also acts in such a way as to press the rod and the stem together against the component to definitively fix their relative positions. This type of lateral connector with adjustable offset does not permit control of the angular position of the stem in relation to the rod, no more than a rotation of the stem in the head, the stem being of partially rectangular cross section. Moreover, in practice, there is no possibility of placing the connection screw in the vertebra after the connector has been positioned on the rod: it often happens that it is necessary to leave part of the screw protruding from the vertebra, which increases the size of the device needlessly and dangerously.
It is an object of the invention to make available to surgeons a type of lateral connector with adjustable offset for a device for stabilizing the spine, connecting a rod and a means for fixing the connector to a vertebra which is quick and easy to fit at any point of the spine, including in the cervical area, and permitting optimum placement of the fixation means under all conditions.
To this end, the subject of the invention is a lateral connector with adjustable offset for providing a connection between a rod of a device for correcting and stabilizing the spine and a fixation member for fixing said device to the spine, such as a screw or a hook, of the type comprising a first component intended to be connected to said fixation member and provided with an extension intended to be inserted in translation into a second component of said connector, said second component being formed by a head which comprises a seat for receiving said rod and means for immobilizing said rod in said seat, said immobilizing means also immobilizing the extension in the second component, characterized in that:
said first component comprises a head provided with an opening which passes right through it and whose lower part has a bearing surface of articulation intended to cooperate with a corresponding bearing surface formed on a head of said fixation member, said extension having a generally cylindrical shape; and in that
said second component comprises an orifice formed in said head for receiving the extension of the first component and permitting a rotation of said second component about the extension, said orifice having an intersection with the bottom of the seat in such a way as to form a slot there, so that a portion of the lateral surface of the extension in the position of insertion protrudes inside the seat.
The head of the first component preferably comprises a lateral aperture allowing said head of the fixation member to be inserted into said opening.
The axis of the seat receiving the rod and the orifice receiving the extension of the first component are preferably oriented obliquely in relation to one another.
Said extension can comprise an at least partially polygonal section forming longitudinal flats on its lateral surface.
Said extension can comprise transverse recesses whose shape matches that of the outer surface of the rod.
Said extension can have a knurled finish on its lateral surface.
Said means for immobilizing the rod in the second component can be formed by a threaded plug cooperating with a thread formed in the head of the second component.
Said head of the second component can have two lateral branches delimiting the seat, the latter being open on the upper face of the head.
The connector according to the invention can comprise means for immobilizing said first component relative to said fixation member.
The opening in said first component can be formed, in its upper part, by an internally threaded hole, and said immobilizing means can be formed by an externally threaded plug.
The invention also relates to an assembly formed by a connector as described above and by a fixation member intended to be implanted on the spine and cooperate with said connector.
Said fixation member intended to be implanted on the spine and adapted to cooperate with a connector for a device for correcting and stabilizing the spine, linking it to a rod, of the type with a spherical head, can be such that said head has, on its upper part, an extension whose upper surface is of spherical shape. Its lower part can be formed by a screw or a hook.
The assembly formed by a connector according to the invention and a fixation member is then such that the plug of the first component has, on its lower face, a spherical bearing surface cooperating with the upper surface of the fixation member.
In another aspect of the present invention, an adjustable lateral connector is provided with two separate components configured in the manner described. The first component comprises a head forming a receiver, in the bottom of which is intended to be placed the head of a fixation member, such as a screw, already anchored or intended to be anchored on a vertebra. The bottom of the receiver and the head of the fixation member are configured in such a way as to allow an articulation of these two components relative to one another in the manner of a ball and socket joint. The head of the first component comprises an extension of substantially cylindrical shape intended to be inserted into the second component of the connector. This second component comprises a head forming a receiver in which is intended to be inserted a substantially cylindrical rod of a device for stabilizing the spine. A threaded plug or any other similar means presses the rod against the bottom of the receiver. The head of the second component comprises an orifice in which the cylindrical extension of the first component is inserted by sliding. This orifice is formed in such a way that a fraction of the surface of the extension, after positioning, opens into the receiver. Thus, the rod of the stabilizing device, when it is pressed against the bottom of the receiver, exerts a pressure on the extension which keeps it in the orifice, at the position chosen by the surgeon. For optimum choice of this position, the surgeon can modify the engagement of the extension in the orifice, which determines the distance between the heads of the first and second components of the connector, and also the angle of rotation of the head of the second component about the extension. Since, in addition, the orientation of the first component relative to the head of the fixation member is free on account of the fact that they are articulated on one another (they can, if appropriate, then be made integral with each other at this orientation), the surgeon has the greatest possible latitude for connecting the rod of the spinal stabilizing device to a given vertebra. In particular, he has very great freedom in choosing the site of implantation of the fixation member, which can be of particular interest for the cervical region.
Another embodiment comprises: a rod; a spinal fixation member; a first connector component including a first head defining a first opening therethrough and an elongated extension, which engages the fixation member in a ball and socket joint arrangement; a second connector component including a second head defining a seat to receive the rod and an orifice intersecting said seat to receive the extension; and a fastener to fix said extension and said rod in contact with one another in said second head.
Yet a further embodiment includes a method, comprising:
providing a lateral connector including a first component with a first head and an extension, and a second component with a second head defining a seat configured to receive a rod and an orifice intersecting the seat; implanting a fixation member in a spine of the patient; receiving the fixation member in the first head;
adjusting position of the first component about the fixation member after said receiving in a first direction of rotational freedom; inserting the extension into the orifice of the second component; translationally adjusting distance between the first head and the second head after said inserting; rotationally adjusting the second head about the extension after said inserting; and fixing the extension and the rod in contact with one another in the second head of the second component.
Alternatively or additionally, this method further includes:
changing position of the first component about the fixation member after said receiving in a second direction of rotational freedom different than the first direction of rotational freedom; removing an end portion of the extension after said inserting; and/or immobilizing the fixation member with respect to the first head after said adjusting and said changing.
In still another form of this method, receiving the fixation member includes engaging an articulating surface of the first head with a spherical surface of the fixation member and the fixation member includes a tooling extension projecting away from said spherical surface, the tooling extension terminating in a spherically shaped upper surface, and wherein said immobilizing includes threading a plug into an opening of the first head to contact the upper surface of the tooling extension.
In yet another form of this method, implantation of the fixation member is performed before receiving it, and the first head includes an opening therethrough intersected by a lateral notch to receive the fixation member by laterally sliding an upper head portion of the fixation member into the first head through the lateral notch.
Further embodiments, objects, features, benefits, advantages, aspects, and forms of the present invention shall become apparent from the description and figures provided herewith.